This invention relates to a small filter consisting of plastic with a housing manufactured by injection molding in which a filter membrane connected in a leakproof manner in its edge area to the housing is positioned between an inlet and an outlet and also relates to a method of manufacturing such a small filter consisting of plastic. Such small filters in accordance with the state of the art are used especially as front attachments for injectors for the sterile filtration of very small amounts. In such instances the total length of the filter housing between the inlet end and the outlet end is approximately 20 mm and the filter diameter approximately 3-5 mm. The filter membrane is connected thereby on an inner shoulder of the filter housing by ultrasonic welding, sealing or adhesion. The manufacture of these filters needs to be improved since several work steps are necessary until the final completion of the filter using the very small individual parts. The subsequent positioning of the stamped-out filter membranes in the finished filter housings and their leakproof connection is very difficult and the part rejects rates are correspondingly high. The finished filter must generally be subjected to sterilization prior to use.
It is known from U.S. Pat. No. 4,113,627 that the filter membrane can be connected in a multipartite filter housing in several work steps by means of liquid plastic to the finished injection-molded part of plastic by injection and is also known that the filter membrane can be positioned between two finished housing parts of plastic and that all three parts (housing parts and filter membrane) can be extrusion-coated in common in a form tool on the edges with liquid plastic; however, this manufacture is very complicated on account of the many individual parts and manufacturing steps.
The inventor therefore has the problem of simplifying the manufacture of such small filters, especially the connection of the filter membrane to the housing and of improving the leakproof connection between filter membrane and housing thereby.